I did and had one for about 5 or 6 years.
Your intial choice is franchise into an exiting one, (no longer put down by Don Bright, in the past he put down LLCs and franchised prop offices.)
If you franchise and your firm doesn't lower it rates while your competitor does, you are in trouble.
If you have a lot of volume and some cash (much less than 10 million) you can approach a clearing firm and try to get competitive rates. Not easy, volume helps.
Then you have to pay a lawyer to help draft agrrements and become a member of an exchage, invest time and money into risk control and compliance (people and software).
It can be done but with the cut throat nature of the pricing, you better have an edge before you start one.
It is better to run your own show.
By the way I know of one that might be for sale if you are really interested.